EP0759322A1 - Method and installation for dissolving solid materials of a bulbous form in a liquid - Google Patents

Abstract

This method disperses solids, esp. having macromolecular structure, into a homogeneous solution. Solid particles in the form of nodules forming a substance in solution, are initially size-reduced. The substance is then agitated over an interval, in a tank (36), holding the particles in suspension in the fluid, with cooling. The substance is pumped away continuously. Particles in the fluid are size-reduced a second time. The substance is introduced into a vessel (43), residing for a set interval under agitation, with the solid particles in suspension. It is then pumped away from the vessel. The particles in the fluid are size-reduced for a third time, and the resulting homogeneous solution is supplied to further processing. Also claimed is a corresponding plant to carry out the process.

Description

The present invention relates to a method for dissolving bulbous solids in liquids according to the preamble of claim 1, and to a plant for carrying out this method.

Such processes are generally used and required in the chemical, dye, food, pharmaceutical and cosmetic industries. This method is also particularly suitable for the gentle dissolution of derivatized cellulose, which is a glucose polymer and has a degree of polymerization of approximately 400.

A possibility of derivatization of cellulose is its xanthation, i.e. its reaction with sodium hydroxide solution and CS ₂ to sodium cellulose xanthate. The xanthate mixture consists of sodium cellulose xanthate and sodium hydroxide solution, the sodium cellulose xanthate initially being present in the mixture in the form of solid particles as a broad spectrum of tubers of different sizes.

With the known methods, these tubers can be loosened and processed into a homogeneous solution.

To dissolve the viscose, especially one-step dissolving processes and systems for carrying out this process are known. In the accompanying Fig. 1, a known system is shown schematically, with which the corresponding one-step dissolving process can be carried out. This system consists of a cylindrical vessel 1, which is provided with a cooling jacket. In the bottom area of the cylindrical vessel 1, a paddle wheel 3 is arranged, which is driven in rotation by a drive motor, not shown, and which is surrounded by an annular sieve 5. Above the screen 5, a cooled insert 6 with cross tubes 7 is arranged as a double jacket. The batch-wise loading of the cylindrical vessel 1 takes place from above through the connection 8, the one to be solved Mixture takes place in a known manner from an xanthation plant. Here, the interior of the insert 9 is filled. The internal circulation of the mixture takes place through the paddle wheel 3, which draws the mixture from the interior, through the sieve 5 into the exterior, from where the medium can flow back through the cross tubes 7 and via the crown of the cooled insert 6 into the interior. The solution is removed from the annular outer space 10.

A device for suctioning off the solvent vapors is provided in the cylindrical vessel 1. These extracted solvent vapors are added to the exhaust system and have to be recovered here, which requires complex equipment.

FIG. 2 shows a sectional view of the lower region of the cylindrical vessel 1 according to FIG. 1, from which it can be seen that the tubers to be loosened are ground between the corrugated base 11 and the inclined rotor blades 12 of the impeller 3 and between the impeller 3 and the sieve 5 will. In order to avoid blockages of the screen 5, a relatively coarse perforation of the screen 5 is required. The mixture is circulated until the desired homogeneity is reached, after which it is pumped out via the pump 13, can be discharged through the valve 14 and the line for further processing, as can be seen from FIG. 1.

In order to increase productivity and in particular to avoid major interruptions in the quantity of solution produced, two corresponding systems can be connected in parallel, as can also be seen in FIG. 1.

Furthermore, it can be provided that the solution removed from the annular outer space 10 can be returned to the container 1 via a cooler 15. This is particularly necessary when, due to the high viscosity of the dissolved xanthate content, a pronounced laminar flow results during the circulation, which is known to have low heat transfer effects and consequently the cooling capacity in the container is too low.

One problem with the one-step process is that the solution engine has enormous peaks in power consumption in the short term. On the one hand, this requires correspondingly large installations for the energy supply and, on the other hand, an excessive load on the power grid.

Multi-stage processes are also known. A system for carrying out such a multi-stage process is shown in FIG. 3, for example. This system is constructed essentially identically to that in FIG. 1, an additional grater 17 being inserted in the return line.

Known grinders are shown in FIGS. 4a, 4b and 5a, 5b. 4 has a paddle wheel 18 which rotates in a housing 19. Stator blades 20 are arranged around the impeller 18. The solution with the tubers to be shredded is supplied via the feed line 21, passes between the rotor blades 22 of the impeller 18 through the stator blades 20 into the outer space 23 and is led away via the discharge line 24.

5 operates similarly, with its impeller 25 being disc-shaped with a corrugated surface 26. This surface 26 interacts with a correspondingly mounted disc 28 on the housing 27 with a corrugated surface 29.

The disadvantage of these two grinders is that the gap width is fixed and therefore no adjustment to the tuber size is possible. Furthermore, these grinders have no pumping action and must therefore be able to flow freely. The housings are not ideally designed in terms of flow technology, so that flow stagnation can occur.

A disadvantage of these known methods is in particular that large tubers, which may be in the mixture, cannot be processed or can only be processed with difficulty. The sieve perforation of the sieve 5 must be chosen appropriately coarse, as a result of which the circulation in the container 1 and the recirculation by grater 17 and / or cooler 15 are repeated several times must become. The energy required for this is large, and the solution must be heated up and cooled accordingly. This harbors the danger that the ripening process and thus the formation of jellies or early coagulation can be triggered in the already dissolved xanthate.

The viscose obtained with such processes should have the "right" degree of maturity. However, this is difficult to achieve, in particular because of the different flow resistances, as a result of which the residence time of the substance to be processed in the systems is also different, so that coagulation can already take place, but this is not desired.

Another major problem arises because the viscose contains coagulum components on the one hand, but on the other hand not all xanthate particles are dissolved, that these two components have to be filtered out by subsequent filtration systems, so these substances are lost for the manufacturing process. These parts also have to be disposed of.

In the case of business interruptions, which can have various reasons, there is the problem that the viscose coagulates in the known methods and systems. The consequence of this is that the corresponding system has to be cleared out after each interruption in operation. In addition to the loss of the materials used, which still have to be disposed of, this also results in complex cleaning work.

In order to achieve good production quality, the systems must be optimally regulated, which results in a certain start-up time. The products manufactured during this start-up period are of insufficient quality and must be disposed of.

A first object of the present invention is to provide a method with which the aforementioned disadvantages are avoided and which enables a mixture of bulbous solids and a liquid to be processed gently into a homogeneous liquid, in particular reducing energy consumption becomes, the product yield increases and there is no coagulation during short downtimes.

According to the invention, this object is achieved by the features of method claims 1 to 3.

Another object of the invention is to provide a system for carrying out the method, which in particular permits optimal adjustment and in which the start-up time is short.

According to the invention, this is solved by the features of claim 4, advantageous embodiments of the invention resulting from the further dependent claims.

The compact design of the plant and the avoidance of poorly flowed rooms in the plant ensure that the duration of the substance in the plant is essentially constant. As a result, the achievable degree of maturity of the viscose is essentially uniform during the entire production phase.

As a result of the closed system, the added carbon disulfide remains in the substance. This enables a post-reaction of the xanthation while the substance is passing through the plant. This results in an improvement in the quality of the viscose.

Since the coagulation at a temperature below 20 ° C is relatively small in the system according to the invention, the cooling is efficient because of the still low viscosity of the substance, which lowers the energy requirement, the system does not have to be emptied and cleaned in the event of an interruption in operation (up to about 12 hours) will.

The method according to the invention and a system for carrying out this method are explained in more detail below by way of example with reference to the accompanying drawing.

• Fig. 6 in schematischer Darstellung den Aufbau einer Anlage zur Durchführung des erfindungsgemässen Verfahrens;
• Fig. 7 eine Schnittdarstellung der ersten Einrichtung zur mechanischen Zerkleinerung der in der Flüssigkeit enthaltenen Feststoffpartikel;
• Fig. 8 eine Schnittdarstellung entlang Linie VIII-VIII der Einrichtung gemäss Fig. 7;
• Fig. 9 eine Schnittdarstellung einer ersten Ausführungsform eines Tanks;
• Fig. 10 eine Schnittdarstellung einer zweiten Ausführungsform eines Tanks;
• Fig. 11 eine Schnittdarstellung durch eine zweite bzw. dritte Einrichtung zur Zerkleinerung der in der Flüssigkeit enthaltenen Feststoffpartikel;
• Fig. 12 eine Ansicht auf die Rotorschaufeln (Fig. 12 unten) und auf die Statorschaufeln (Fig. 12 oben), aufgenommen entlang Linie XII-XII durch die Einrichtung gemäss Fig. 11;
• Fig. 13 in vergrösserter Darstellung das Zusammenwirken der Rotorschaufeln und der Statorschaufeln der Einrichtung gemäss Fig. 11.

It shows:

• 6 shows a schematic representation of the structure of a plant for carrying out the method according to the invention;
• 7 shows a sectional illustration of the first device for mechanical comminution of the solid particles contained in the liquid;
• 8 shows a sectional illustration along line VIII-VIII of the device according to FIG. 7;
• 9 is a sectional view of a first embodiment of a tank;
• 10 is a sectional view of a second embodiment of a tank;
• 11 shows a sectional view through a second or third device for comminuting the solid particles contained in the liquid;
• FIG. 12 shows a view of the rotor blades (FIG. 12 below) and the stator blades (FIG. 12 above), taken along line XII-XII through the device according to FIG. 11;
• 13 is an enlarged view of the interaction of the rotor blades and the stator blades of the device according to FIG. 11.

As can be seen from FIG. 6, alkaline cellulose, an alkali and carbon disulphide are fed into a xanthation device 31 to produce a viscose solution, as shown by the arrows 32. From the xanthation device 31, the substance to be processed, which consists of a liquid in which solid particles are present in the form of tubers, passes via a feed line 33 into a first device 34 for the first mechanical comminution of the solid particles contained in the liquid. Here the tubers are crushed for the first time, as will be described in more detail later. From this device, the substance reaches a tank 36 via a discharge line 35. This tank 36 is equipped with a device 37 for cooling the substance, and with an agitator 38.

The substance remains in this tank 36 for a while, during which it is stirred by the agitator 38, so that the solid particles in the liquid are kept in suspension and the substance is cooled. During this dwell time and by stirring, the process of dissolving the solid particles in the liquid is supported.

The substance is continuously pumped out of this tank 36 via a first line 39 by a pump 40. The substance then passes through a second device 41 for mechanical comminution of the solid particles contained in the liquid. The substance is passed through a second line 42 into a container 43 which is equipped with a further agitator 44. Integrated in the second line 42 is a device 45 for cooling the substance, which is designed in a known manner as a heat exchanger.

The substance remains in the container 43 for a certain time, during which it is stirred, so that the solid particles in the liquid are kept in suspension, which in turn supports the chemical dissolving process.

The substance is pumped out via a third line 46 by a second pump 47 and fed to a third device 48 for further mechanical comminution of the solid particles contained in the liquid. After this third mechanical comminution, the substance now present as a practically homogeneous solution passes through a further discharge line 49 and can be fed to further processing.

When the tank 36 is loaded in batches from the xanthation device 31, a second device of this type can advantageously be used be provided, the charge of which can also reach the tank 36 via the feed line 33, as shown by the dash-dotted arrow 50.

Between the second line 42 and the discharge line 35, a connecting line 51 is inserted, which is shown in broken lines and can be opened and closed with a valve (not shown), so that, if necessary, part of the substance from the second line 42 is returned to the tank 36 can be.

As can be seen from FIG. 7, the first device for mechanical comminution of the solid particles contained in the liquid consists of a housing 52 which has the corresponding supply line 33 and discharge line 35. The substance flows through a space 53 which is formed by the housing 52. Two shafts 54 and 55 are arranged in this space, which run parallel to one another and which can be driven in rotation. Knives 56, which are arranged one behind the other and spaced apart from one another, are fastened on each shaft 54 and 55 and form a star shape, which in the present case consists of four blades 57. The knives 56 on each shaft 54 and 55 are each offset by 30 degrees from one another, so that the blades 57 form a helix along the shafts 54 and 55, respectively.

As shown in FIG. 8, a knife 56 of one shaft 54 or 55 comes to lie in the space formed by two knives 56 of the other shaft 55 or 54. This means that the knives 56 overlap in the space 53 through which the substance flows. The two shafts 54 and 55 with the knives attached to them are set in rotation via drive motors 58 and drive belts 59, the direction of rotation being opposite and the speed of rotation being different.

With this device, even large tubers that are in the liquid can be mechanically crushed before they get into the tank 36.

The tank 36, as shown in FIG. 9, has an insulating jacket 60, which is equipped with cooling channels 61, in which a coolant can circulate. After it has passed through the first device 34, the substance arrives in the tank 36 via the discharge line 35. A vertical shaft 62 is arranged centrally in the tank 36, on which paddle wheels 63 are fastened, which are located within flow guide tubes 64, which are arranged via struts 65 which are attached to the tank 36 are held. By rotating the vertical shaft 62, a downward axial flow of the substance is achieved in the central region of the tank 36, which is deflected in the region of the tank bottom 66 and flows upwards in the outer region of the tank. This deflection is supported by a disc agitator 67, which forms part of the tank bottom. There is a gap 68 between the disk of the disk agitator 67 and the tank bottom 66, the width of which can be selected or adjustable such that only solid particles with a maximum size can reach the lower region 69 of the tank 36. In this area 69, the substance is stirred and kept in motion by blades attached to the disc agitator 67, so that no sedimentation can take place. From there, the substance can be pumped out and passed on.

As can be seen from FIG. 10, the tank 36 can have compartments 70, 71 and 72 lying one above the other. Through these compartments 70, 71, 72 runs a rotatably drivable through shaft 73, on which one or more paddle wheels 74 are fastened in each compartment 70, 71, 72 and which is arranged in a current guide tube corresponding to the current guide tube 64 in FIG. 9. In each compartment 70, 71 and 72 a downward axial flow is thus achieved in the central area, which is deflected in the lower area of the compartments 70, 71, 72 and flows upwards in the outer area. Each compartment floor 75, 76 and 77 is equipped with a disk agitator 78, which has the same structure as the disk agitator 67 according to FIG. 9. Here, the gap width between the disk agitators and the corresponding compartment floors is set so that it decreases from top to bottom , whereby the size of the solid particles to be let through when passing through this tank 36 becomes smaller from top to bottom, depending on the gap width. The substance that gets into the lower region 79 of this tank 36 is then pumped out.

An embodiment of the second device 41 for mechanical comminution of the solid particles contained in the liquid is shown in FIGS. 11 to 13. This consists of a spiral housing 80, in which a rotating impeller 81 is arranged. The impeller 81 is equipped on the input side with a worm 82 which is designed as a knife, as a result of which larger solid particles entering can still be cut open. The impeller 81 is equipped with rotor blades 83, which are arranged in a plurality of annular steps 84, 85, 86 and lie essentially in a radial plane. Stator blades 87 are fastened to the spiral housing 80 and are likewise arranged in three annular stages 88, 89, 90, each stage of stator blades 87 coming to lie between two stages of rotor blades 83. Rotor blades 83 and stator blades 87 taper to a point in the oppositely directed region, as can be seen in particular from the enlarged illustration according to FIG. 13.

The impeller 81 can be displaced in the axial direction in a known manner via adjustment means, not shown. As a result, the gap width between rotor blades 83 and stator blades 87 can be set, as a result of which the solid particles in the substance passing through this device 41 are more or less comminuted, depending on the gap width.

The rotor blades are oriented inclined with respect to the radial direction, as a result of which a pumping effect is achieved, so that the solid particles and the liquid must inevitably flow through this device.

With this device, the solid particles contained in the liquid are broken up to a size of up to 10 mm and divided into particles of less than 2 mm. The particles are not broken up and the mechanical destruction of the xanthate structure is avoided.

The third device 48 for further comminuting the solid particles in the liquid can be designed in an identical manner to the device shown in FIGS. 11 to 13, the gap width being set to be smaller becomes. This means that the solid particles can be crushed to such an extent that they completely dissolve in the subsequent ripening stage.

An embodiment of such a system is of such a size that the flow rate of the substance is approximately 50 m ³ / h. This can produce about 4 to 5 tons of dry fibers per hour.

With such systems according to the invention, small quantities can also be produced.

With this method according to the invention and the installation for carrying out this method, a gentle treatment of the substance and in particular the solid particles during its comminution is achieved, whereby the quality of the viscose obtained subsequently can be increased and the product yield is increased.

As already mentioned, the method and the system, as described above in detail, are not limited to this exemplary embodiment, but can be used for similar substances in which bulbous solids are to be dissolved in liquids, as is generally the case in chemistry, the dye, food, pharmaceutical and cosmetic industries will be the case.

Claims (12)

Method for dissolving bulbous solids in liquids to achieve an essentially homogeneous solution, in particular for dissolving solids with macromolecular structures in a solvent liquid, characterized in that the solid particles in the form of tubers, which are contained in the liquid and form a substance with it, are crushed for the first time; thereafter the substance remains in a tank (36) while stirring the substance, keeping the solid particles in the liquid in suspension and cooling the substance; the substance is pumped out essentially continuously from the tank (36) and the already reduced solid particles contained in the liquid are crushed a second time; the substance is passed into a container (43) in which it remains for a certain time while the substance is being stirred and the solid particles in the liquid are kept in suspension; the substance is pumped out of the container (43) and the already reduced solid particles contained in the liquid are crushed a third time; the practically homogeneous solution thus obtained is fed for further processing. A method according to claim 1, characterized in that at least part of the substance is returned to the tank (36) after the solid particles contained in the liquid have been crushed a second time. A method according to claim 1 or 2, characterized in that the substance is cooled after the solid particles contained in the liquid have been crushed a second time and before it is introduced into the container (43). Installation for carrying out the method according to one of claims 1 to 3, characterized in that: it is designed as a closed system; a first device (34) is provided with a feed line (33) and discharge line (35) for the first mechanical comminution of the solid particles contained in the liquid, the discharge line (35) of which opens into the tank (36); the tank (36) is equipped with an agitator (38) and a device (37) for cooling the substance; a first line (39) is connected to the tank (36), which connects it to a second device (41) for the second mechanical comminution of the solid particles contained in the liquid, a first pump (40) being interposed; a second line (42) leads from the second device (41) to the second mechanical comminution into the container (43), which is equipped with a further agitator (44); a third line (46) is connected to the container (43), which leads to a third device (48) for the third mechanical comminution, and in which a second pump (47) is interposed; the third device (48) for the third mechanical comminution is provided with a further derivation (49) through which the practically homogeneous solution can be derived and fed to further processing. Installation according to Claim 4, characterized in that a branching provided with a valve is inserted into the second line (42), to which a connecting line (51) is connected which leads into the tank (36). System according to claim 4 or 5, characterized in that a device (45) for cooling, which is designed as a heat exchanger, is inserted into the second line (42). Plant according to one of claims 4 to 6, characterized in that the first device (34) for the first mechanical comminution consists of a housing (52) which forms a space (53) between the feed line (33) and the discharge line (35) through which the substance flows, into which space (53) wings (57) of knives (56) protrude, the knives (56) being spaced from each other on two parallel, rotatably drivable shafts (54, 55) that the wings (57) the knives (56) form a regular star shape on each shaft (54, 55) and each knife (56) is offset from the neighboring one by an angle of rotation, and that the wings (57) of the knives (56) of the one shaft (54 or 55) each protrude into the space between two spaced apart knives (56) of the other shaft (55 or 54). System according to one of claims 4 to 7, characterized in that the tank (36) has an insulating jacket (60) and is provided with cooling channels (61) with a coolant circulating therein, that the agitator (38) consists of several paddle wheels (63 ), which are fastened on a vertical shaft (62) at a distance from one another and are located in flow guide tubes (64), as a result of which a downward axial flow can be achieved in the central region of the tank (36), in order to support the deflection of the downward axial flow a disc agitator (67) is provided in an upward flow in the region of the tank bottom (66), a gap (68) existing between the disk and the tank bottom (66). Installation according to claim 8, characterized in that the tank (36) is divided into a plurality of compartments (70, 71, 72) lying one above the other, and in each compartment (70, 71, 72) at least one seated on the continuous shaft (73) Paddle wheel (74) is arranged, and that the individual compartments (70, 71, 72) are each separated from one another by a disk agitator (78), there being a distance between the respective disk and the corresponding compartment bottom (75, 76, 77). Plant according to one of claims 1 to 9, characterized in that the second device (41) for mechanical comminution and the third device (48) for mechanical comminution each consist of an impeller (81) rotating in a spiral housing (80), which with Rotor blades (83) is equipped, which are arranged in several annular stages (84, 85, 86) on the impeller (81) and essentially in a radial Plane, and which cooperate with stator blades (87), which are also fixed in a ring in several steps (88, 89, 90) on the volute (80), each step (88, 89, 90) of stator blades (87) between two stages (84, 85, 86) of rotor blades (83) come to rest and the rotor blades (83) are inclined with respect to the radial direction. Installation according to claim 10, characterized in that a worm (82) is arranged on the shaft of the impeller (81) in the entry area and is designed as a knife on the entry side. Installation according to claim 10 or 11, characterized in that both the rotor blades (83) and the stator blades (87) are tapered in the mutually directed area, and that the impeller (81) is displaceable in the axial direction by means of adjusting means, so that the Gap width between the rotor blades (83) and stator blades (87) is adjustable.

Images